The present invention relates to a fast setting adhesive composition of the two-part separate application type. More specifically, the present invention relates to a fast setting adhesive composition of the two-part separate application type comprising solutions A and B, wherein the solution A is an aqueous solution of a natural or synthetic high polymer having an amide bond (--CO--NH-- structure) or an imide bond ##STR1## within the molecule, or an aqueous dispersion obtained by adding a rubber latex and/or synthetic resin emulsion to the aqueous solution of the natural or synthetic high polymer, and the solution B is an aqueous solution of a water-soluble dialdehyde compound, or an aqueous solution or dispersion obtained by adding a crosslinking agent for crosslinking the high polymer to the aqueous solution of the water-soluble dialdehyde compound. In order to bond two members together with an adhesive of this composition, the solution A is applied on one surface of one of the members, the solution B is applied to one surface of the other member, the two surfaces are brought into contact, and both members are pressed together. The adhesive composition allows fast setting with the excellent initial green bonding strength such that the two surfaces are bonded to each other with a significant strength within a few minutes.
In the lumber industry, there has been recently proposed to perform continuous mass-production with a conveyor system. In view of such a proposal, a fast setting adhesive has been desired. Although a cyanoacrylate-type instantaneous adhesive may be used, it is too costly. A fast setting adhesive of the two-part separate application type has long been commercially available which contains a urea resin-type adhesive as component A and a mixture of a strong acid such as phosphoric acid with an aqueous solution of a high polymer such as polyvinyl alcohol (PVA) as component B. However, the strong acid accelerates aging of the urea resin and degrades the strength of the wood material. Accordingly, this type of adhesive is not widely accepted.
The present inventors have previously proposed a gel composition comprising an aqueous solution of a mixture of a high polymer having an amide bond or an imide bond within the molecule with a dialdehyde compound such as glyoxal, wherein the gel composition turns into a sol like a glue when heated to a temperature of 70.degree. to 90.degree. C. and it turns into a gel when cooled to 40.degree. to 50.degree. C. A water-soluble high polymer having such a bond can be a water-soluble protein such as casein which has an amide bond within the molecule (Japanese Patent Publication No. 55-17066), or a high polymer having a maleinimide bond within the molecule (Japanese Patent Publication No. 55-17057). The gel compositions which are reversible under heating as described above can be handled in a similar manner as a glue and may be effectively used as fast setting adhesives. However, these gel compositions must be heated to 70.degree. to 90.degree. C. when it is used, and may not be easily mixed with a rubber latex or a synthetic resin emulsion so that they are poor in water resistance.